The present invention relates generally to computer controlled engine systems and, more particularly, to a method and apparatus for performing engine control operations in response to limited control signals generated by an engine control computer. While the present invention is applicable to ignition systems, fuel injection systems and other operating systems of an internal combustion engine, it will be described with reference to a fuel injection system for which it is initially intended.
Computer engine controllers must monitor a variety of input signals representative of the operating conditions of engines which they are controlling. Based on these input signals, the controllers determine ignition times and fuel injection times and durations which in turn are used to control engine ignition systems and fuel injection systems. While the computers are particularly adept at signal acquisition and utilization of engine operating signals to calculate engine control signals, the computers also typically use the signals to control the engine systems.
Unfortunately, the computers tend to be less adept at controlling engine systems and hence these operations require an inordinate amount of the processing time of the computers. The burden of performing these control operations, such as the control of fuel injectors, becomes more and more troublesome as the computers are required to perform more and more operations due to tighter engine control requirements.
There is thus a need for an auxiliary controller which can reduce the processing load of engine control computers to enable the computers to perform evolving and more complicated engine control calculations. Preferably, such an auxiliary controller would be universal, i.e. readily configurable for a large variety of engines such that a single controller could be provided for many applications. It is apparent that a single controller part which can be used on a large variety of engines would result in reduced costs both due to increased numbers of the part made and also to reduced inventory requirements, of a single part. An additional attractive feature would be a computer fault mode which would enable engine operation, albeit of a limited nature, in the event of failure of that portion of a computer which controls the auxiliary controller.